Make largest four sums of rows in an matrix zero

Currently I have code to make the row with the maximum sum in the matrix equal zero, however I need to make the four largest sum rows equal zero. How do I go about doing this? Below is my current code:

A=createsrandomnetwork(10,3);
U=sum(A)    %sum of matrix rows
M=max(U)
maxsum = max(U);  
A(U == maxsum, :) = 0; %rows and columes 
A(:, U == maxsum) = 0;
A(U > M, :) = 0;
A(:, U > M) = 0

[Alexandra Harkai]

What result are you expecting when there are more than one rows with the maximum sum? This leads to the question of what you exactly mean by 'four largest sum rows'?

For example, what would be the four largest if your row sums are 2,2,2,3,3?